1. Field of the Invention
This invention relates to copy protection and usage control systems for computer software.
2. Description of the Prior Art
Various copy protection systems for computer software have been developed in the art. See, for example, Chandra et al., U.S. Pat. Nos. 4,644,493 and 4,903,296.
The basic form of these systems prevents a user from making a copy of a magnetic medium, such as a floppy disk, embodying the software which is to be protected. Other protection systems have been developed which restrict the us of the software to a single computer system. For example, software has been sold in combination with a hardware device which must be plugged into the computer's communication port before the software can be run. See, for example, Chou et al., U.S. Pat. No. 4,562,306. Encryption of codes stored in a ROM or secure coprocessor built into the user's computer have also been used for this purpose. See, for example, Karp, U.S. Pat. No. 4,866,769.
Variations of the foregoing techniques have allowed software distributors to control the length of time or the number of times a user can run protected software. See, for, example, Comerford et al., U.S. Pat. No. 5,109,413, and William. U.S. Pat. No. 4,740,890. These techniques have been developed to provide a trial period during which a potential purchaser can decide whether or not he or she wants to buy the software. After the trial period, either new software without the usage control system has been provided or instructions have been given to the user to disable the usage control system.
Although these approaches have to some extent imparted a limited life to computer software, they have not provided truly consumable software in the sense that a student workbook, a cross-word puzzle book, a game book, or a scholastic test is consumable. Consumable software would be of great value to the software industry, as well as to software purchasers, since it would allow software to be marketed on a finite usage basis rather than an unlimited usage basis. This would allow the purchaser to acquire only the amount of usage necessary to satisfy his or her needs, and would allow the software distributor to adjust the cost of the software to reflect the limited usage being provided.